/*
 * 
 * WebGL Versuch von Alex
 * 
 */

var gl;

function initGL(canvas) {
	try {
		gl = canvas.getContext("experimental-webgl");
		gl.viewportWidth = canvas.width;
		gl.viewportHeight = canvas.height;
	} catch (e) {
	}
	if (!gl) {
		alert("Could not initialise WebGL, sorry :-(");
	}
}


function getShader(gl, shader_type, shader_source) {
    var shader;

    /* Shader erzeugen */
    shader = gl.createShader(shader_type);

    /* Shaderquelltext laden und kompilieren */
    gl.shaderSource(shader, shader_source);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        window.alert("Compiling Error: "+gl.getShaderInfoLog(shader));
        return null;
    }

    return shader;
}


var shaderProgram;

function initShaders() {
	var fragmentShader;
	var vertexShader;
	
	fragmentShader = getShader(gl, gl.FRAGMENT_SHADER, shaderprogram_fragmentshader);
    vertexShader = getShader(gl, gl.VERTEX_SHADER, shaderprogram_vertexshader);

	shaderProgram = gl.createProgram();
	gl.attachShader(shaderProgram, vertexShader);
	gl.attachShader(shaderProgram, fragmentShader);
	gl.linkProgram(shaderProgram);

	if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
		alert("Could not initialise shaders");
	}

	gl.useProgram(shaderProgram);

	shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
	gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);

	shaderProgram.vertexColorAttribute = gl.getAttribLocation(shaderProgram, "aVertexColor");
	gl.enableVertexAttribArray(shaderProgram.vertexColorAttribute);

	shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
	shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
}


var mvMatrix = mat4.create();
var mvMatrixStack = [];
var pMatrix = mat4.create();

function mvPushMatrix() {
	var copy = mat4.create();
	mat4.set(mvMatrix, copy);
	mvMatrixStack.push(copy);
}

function mvPopMatrix(){
	if(mvMatrixStack.length == 0){
		throw "Invalid popMatrix!";
	}
	mvMatrix = mvMatrixStack.pop();
}

function setMatrixUniforms() {
	gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
	gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
}


var pyramidVertexPositionBuffer;
var pyramidVertexColorBuffer;
var cubeVertexPositionBuffer;
var cubeVertexColorBuffer;
var cubeVertexIndexBuffer;

function initBuffers() {
	/*** Pyramid ***/
	// Position
	pyramidVertexPositionBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, pyramidVertexPositionBuffer);
	var vertices = [
        // Front face
        0.0,  1.0,  0.0,
       -1.0, -1.0,  1.0,
        1.0, -1.0,  1.0,

       // Right face
        0.0,  1.0,  0.0,
        1.0, -1.0,  1.0,
        1.0, -1.0, -1.0,

       // Back face
        0.0,  1.0,  0.0,
        1.0, -1.0, -1.0,
       -1.0, -1.0, -1.0,

       // Left face
        0.0,  1.0,  0.0,
       -1.0, -1.0, -1.0,
       -1.0, -1.0,  1.0
	];
	gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
	pyramidVertexPositionBuffer.itemSize = 3;
	pyramidVertexPositionBuffer.numItems = 12;

	// Color
	pyramidVertexColorBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, pyramidVertexColorBuffer);
	var colors = [
          // Front face
          1.0, 0.0, 0.0, 1.0,
          0.0, 1.0, 0.0, 1.0,
          0.0, 0.0, 1.0, 1.0,

          // Right face
          1.0, 0.0, 0.0, 1.0,
          0.0, 0.0, 1.0, 1.0,
          0.0, 1.0, 0.0, 1.0,

          // Back face
          1.0, 0.0, 0.0, 1.0,
          0.0, 1.0, 0.0, 1.0,
          0.0, 0.0, 1.0, 1.0,

          // Left face
          1.0, 0.0, 0.0, 1.0,
          0.0, 0.0, 1.0, 1.0,
          0.0, 1.0, 0.0, 1.0
	];
	gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);
	pyramidVertexColorBuffer.itemSize = 4;
	pyramidVertexColorBuffer.numItems = 12;

	/*** Cube ***/
	// Position
	cubeVertexPositionBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
	vertices = [
        // Front face
        -1.0, -1.0,  1.0,
         1.0, -1.0,  1.0,
         1.0,  1.0,  1.0,
        -1.0,  1.0,  1.0,

        // Back face
        -1.0, -1.0, -1.0,
        -1.0,  1.0, -1.0,
         1.0,  1.0, -1.0,
         1.0, -1.0, -1.0,

        // Top face
        -1.0,  1.0, -1.0,
        -1.0,  1.0,  1.0,
         1.0,  1.0,  1.0,
         1.0,  1.0, -1.0,

        // Bottom face
        -1.0, -1.0, -1.0,
         1.0, -1.0, -1.0,
         1.0, -1.0,  1.0,
        -1.0, -1.0,  1.0,

        // Right face
         1.0, -1.0, -1.0,
         1.0,  1.0, -1.0,
         1.0,  1.0,  1.0,
         1.0, -1.0,  1.0,

        // Left face
        -1.0, -1.0, -1.0,
        -1.0, -1.0,  1.0,
        -1.0,  1.0,  1.0,
        -1.0,  1.0, -1.0
	];
	gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
	cubeVertexPositionBuffer.itemSize = 3;
	cubeVertexPositionBuffer.numItems = 24;

	// Color
	cubeVertexColorBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexColorBuffer);
	colors = [
        [1.0, 0.0, 0.0, 1.0], // Front face
        [1.0, 1.0, 0.0, 1.0], // Back face
        [0.0, 1.0, 0.0, 1.0], // Top face
        [1.0, 0.5, 0.5, 1.0], // Bottom face
        [1.0, 0.0, 1.0, 1.0], // Right face
        [0.0, 0.0, 1.0, 1.0]  // Left face     
	];
	
	var unpackedColors = [];
	for (var i in colors){
		var color = colors[i];
		for (var j=0; j<4; j++){
			unpackedColors = unpackedColors.concat(color);
		}
	}
	gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(unpackedColors), gl.STATIC_DRAW);
	cubeVertexColorBuffer.itemSize = 4;
	cubeVertexColorBuffer.numItems = 24;
	
	// Index
	cubeVertexIndexBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
	var cubeVertexIndices = [
         0, 1, 2,      0, 2, 3,    // Front face
         4, 5, 6,      4, 6, 7,    // Back face
         8, 9, 10,     8, 10, 11,  // Top face
         12, 13, 14,   12, 14, 15, // Bottom face
         16, 17, 18,   16, 18, 19, // Right face
         20, 21, 22,   20, 22, 23  // Left face 
	];
	gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
	cubeVertexIndexBuffer.itemSize = 1;
	cubeVertexIndexBuffer.numItems = 36;
}

function degToRad(degrees) {
	return degrees * Math.PI / 180;
}


// Rotationsvariablen
var rPyramid = 0;
var rCube = 0;

function drawScene() {
	gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
	gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

	mat4.perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0, pMatrix);

	mat4.identity(mvMatrix);

	/**** Pyramid ****/
	mat4.translate(mvMatrix, [-1.5, 0.0, -10.0]);
	
	mvPushMatrix();
	mat4.rotate(mvMatrix, degToRad(rPyramid), [0, 1, 0]);
	
	gl.bindBuffer(gl.ARRAY_BUFFER, pyramidVertexPositionBuffer);
	gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, pyramidVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

	gl.bindBuffer(gl.ARRAY_BUFFER, pyramidVertexColorBuffer);
	gl.vertexAttribPointer(shaderProgram.vertexColorAttribute, pyramidVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);

	setMatrixUniforms();
	gl.drawArrays(gl.TRIANGLES, 0, pyramidVertexColorBuffer.numItems);
	
	mvPopMatrix();

	/**** Cube ****/
	
	mat4.translate(mvMatrix, [3.0, 0.0, 0.0]);
	
	mvPushMatrix();
	mat4.rotate(mvMatrix, degToRad(rCube), [1, 1, 1]);
	
	gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
	gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, cubeVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

	gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexColorBuffer);
	gl.vertexAttribPointer(shaderProgram.vertexColorAttribute, cubeVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);

	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
	setMatrixUniforms();
	
	//gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems);
	gl.drawElements(gl.TRIANGLES, cubeVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
	
	mvPopMatrix();
}

var lastTime = 0;
function animate(){
	var timeNow = new Date().getTime();
	if(lastTime != 0){
		var elapsed = timeNow - lastTime;
		
		rPyramid += (90 * elapsed) / 1000.0;
		rCube -= (75 * elapsed) / 1000.0;
	}
	lastTime = timeNow;
}

function tick(){
	requestAnimFrame(tick);
	drawScene();
	animate();
}

function webGLStart() {
	var canvas = document.getElementById("lesson02-canvas");
	initGL(canvas);
	initShaders();
	initBuffers();

	gl.clearColor(0.0, 0.0, 0.0, 1.0);
	gl.enable(gl.DEPTH_TEST);
	
	tick();

	//drawScene();
}
